Investigation of effects of high temperature and pressure on a polymer electrolyte fuel cell with polarization analysis and X-ray imaging of liquid water

Polymer electrolyte fuel cells (PEFCs) capable of operation at high temperature are urgently required to downsize the radiators needed in high-power automobiles. The decrease of oxygen partial pressure as a result of high water vapor pressure is a critical problem at high temperature. To achieve high current density under these conditions, pressurization of the feed gas is essential. In this study, the effects of high temperature and high pressure on a PEFC are investigated by polarization analysis and X-ray imaging of liquid water in a membrane electrode assembly. Increasing concentration overpotential and decreasing OCV lead to loss of cell performance at high temperature under ambient pressure. When the gas is pressurized, liquid water accumulation in the gas diffusion layer increases but concentration overpotential decreases. This indicates that liquid water in the substrate layer only weakly affects concentration overpotential. By contrast, liquid water in the microporous layer strongly affects concentration overpotential.